custom from "Etch-servo".
Drives 3 servo motors using a simple parallel-port-attached
circuit.
'freqgen' produces an enable waveform to turn the servo motors at a
variable speed, and 'encoder' reads TTL-level quadrature inputs to close the
loop.

The circuit uses 2 L6205 dual full-bridge driver to control 3 servo motors of a CharlyRobot CNC.
The last free channel will be used for spindel